It has been disclosed that sticky polymers such as ethylene/propylene/diene monomer (EPDM) and polydienes such as polybutadiene (BR), polyisoprene (IR), and styrene-butadiene rubber (SBR) can be produced in gas phase polymerization processes. Such processes are disclosed, for example, in U.S. Pat. Nos. 4,994,534; 5,304,588; 5,453,471; 5,652,304; 5,858,903; 5,877,109; EP 0 657 647; and WO 96/04322 and 04323.
In general, a sticky polymer is defined as a polymer being particulate at temperatures below the sticking or softening temperature but forming agglomerates at temperatures above its sticking or softening temperature. U.S. Pat. Nos. 4,994,534 and 5,304,588 have taught that sticky polymers, such as EPDM and polybutadiene (BR), can be produced in a gas phase polymerization at or above the sticking or softening temperature of the polymer being produced in the presence of a polymerization catalyst when an inert particulate material is used. In the gas phase reactor, the inert particulate material serves to continually coat the surfaces of sticky polymer that is forming, thereby maintaining the bed of forming polymer in a fluidized state. And since the surfaces of the resin produced become non-sticky, they are free-flowing for ease in handling and subsequent formulating or compounding, and readily bulk shippable. Inert particulate materials have been selected from the ingredients employed in rubber formulations and compounding and include carbon black, silica, talc, clay, activated carbon black, modified carbon black, and mixtures thereof The preferred inert particulate materials are carbon black, silica, and mixtures thereof, with a carbon black being the most preferred inert particulate material in gas phase processing.
Carbon black is the primary choice of inert particulate material (also sometimes referred to fluidization aid or flow aid). That is because carbon black aids in the prevention of agglomeration during polymerization and as well as in post reactor processing. And, more importantly, it is almost always employed as a reinforcing/partitioning agent/filler in compounding so its use does not introduced a new ingredient into compounding and/or the final molded or extruded article (e.g., tire (sidewall and/or tread), roofing, or hose). And, its presence ab initio as part of the polymer results in many mixing advantages in compounding--faster, simpler, less labor, cost reductions, etc.
U.S. Pat. Nos. 5,162,463 and 5,200,477 disclose the surface treatment of an inert particulate material such as carbon black with a PDMS (polydimethylsiloxane), PMHS (polymethylhydrogensiloxane), AM-DDMS (alkyl-modified polydimethylsiloxane), or OM-PDMS (an organo-modified polydimethylsiloxane). The inert particulate materials are treated with these compounds to prevent agglomeration and/or reduce stickiness of sticky polymers in the polymerization system.
More recently, it has been disclosed in WO 98/34960 that a "modified carbon black" can be employed for these purposes. A "modified carbon back" is defined on pages 4-5 of the reference. For the most part, this definition defines a modified carbon black as a silicon-treated or silica-coated carbon black or a carbon black having an attached organic group(s). The organic group can be attached via the reaction of a diazonium salt with a carbon black to impart water dispersibility. Other organic groups, according to the reference can include attached aromatic sulfide and aminophenyl groups. It is further suggested in this reference that the use of these modified carbon blacks in a gas phase polymerization will produce a polymer product containing them which, in turn, will result in an article (e.g., hose or tire) having improved properties. Gas phase polymerizations employing these modified carbon blacks and the suggested improvements are not demonstrated.
From the above discussion, it can be seen that the properties of the inert particulate materials can influence the ability to coat the forming polymer and the fluidizability of the bed of the forming polymer. However, the introduction of carbon black as a fluidization aid in a polymerization such as a gas phase polymerization, for example, brings with it a significant problem from a commercial perspective. The use of carbon black can greatly affect the polymerization catalyst.
However, WO 98/34960 does not address the problems discovered and solved by the inventors of this invention. In the present invention, the inventors have found that carbon black, including modified carbon blacks, undesirably consume large amounts of organoaluminum compounds (e.g., co-catalyst). That is, much more co-catalyst is employed than is required for the metal catalyst precursor. It is believed that this additional amount of co-catalyst is consumed in scavenging surface active groups located on the carbon black that can serve as catalyst poisons. Hence, for a gas phase process, the internal surfaces of the gas phase system and the carbon black itself is either pretreated with the same or different co-catalyst employed in the polymerization. Or, alternatively, increased quantities of co-catalyst are utilized during the polymerization itself. There is a need to make the production of sticky polymers more cost-effective by reducing the usage of co-catalyst (organoaluminum compounds).
Thus, for these reasons, there needs to be provided an improved polymerization process and an improved carbon black that not only can coat the forming polymer in the gas phase reactor so that it is fluidizable, but also be one that does not readily consume large amounts of organoaluminum compounds (e.g., co-catalyst). That is, there is a need for an inert particulate material such as a carbon black that improves the activity of the polymerization catalyst by providing a gas phase, solution, slurry, or bulk polymerization which utilizes smaller amounts of catalyst, and especially cocatalyst, so as to result in a commercially more cost effective gas phase polymerization process.